The present invention relates to an ionization smoke detector connected to an alarm circuit triggered by a sensor in the detector when a predetermined smoke level is exceeded. The detector has particular utility as a fire detector in residences since it is battery-operated and the alarm circuit provides warnings for both fires and approaching weak battery conditions.
Ionization smoke detectors such as shown in U.S. Pat. No. 3,728,706, are already well known in the art. Such detectors operate upon the principle that an ionization current catalyzed by a radiation source is affected by the presence of particulate matter such as that found in aerosols or smoke emanating from a fire. The particulates reduce the ionization current and such a reduction in current can be detected and correlated with the density of the particulate matter to provide a fairly accurate indication of a smoke condition.
It is desirable to operate such a detector with a battery, especially in residential homes and apartments. To provide a prominent alarm signal, a pulsating circuit energized by the battery may be triggered by the smoke detector. A pulsating circuit reserves battery strength so that the alarm may continue for an extended period of time even after the life of the battery is partially expended.
In view of the reliance that may be placed upon a smoke detector, particularly in a residential environment, safety considerations must be given careful consideration. The limited life of a battery might suggest that it is not suitable for an alarm device; however, it is also recognized that fire can destroy or cut off outside electrical sources before the fire is detected. The battery-operated system functions independently and can be safely relied upon if it includes low-voltage detection circuitry for sounding the alarm when the battery level is approaching a weakened or marginal condition.
It is, accordingly, a general object of the present invention to disclose a battery-operated ionization smoke detector connected to an alarm circuit possessing features insuring safe operation in the residential environment.